Electrical circuit arrangement for the generation of oscillations



y 15, 1952 E. A. NEWMAN ELECTRICAL CIRCUIT ARRANGEMENT FOR THE GENERATION OF OSCILLATIONS Filed Feb. 14, 1948 fnven for Edward Arthur Newman Afforney Patented July 15, 1952 2,603,750 1 1 ELECTRICAL *omom'r ARRANGEMENT r011 THE GENERATI ON OF OSGILLATIONSZ EdwardfArthur iNewman, Ealing, London, England, assignor to Electric.&TMusical,1 Industries Limited, ,Hayes, England, .a company of great Britain Application-February 1,4,.1948,-jsam N03845:. In :Great'iBi'itain February 28,. 1947 This invention relates to circuit arrangements 'for' :.g enerating electrical z-sawtooth oscillations, and 2more1particularly"butinot exclusively" to ;cir-- 'cuitsi forigenerating :sawtoothcurrentvariations :in' the magnetic idefiection 'coils of -a cathoderray .tubel V I v The. object of :the present invention is to prov vide a circuit .in whichztheirlapid return portions the-sawtooth oscillations ;,are :generated in an improved ormorerapidmanner.

According-to one featureofith -invention there is provided-a :circuitarrangement ion-generating electrical sawtoothoscillationscomprising anamlplifier in :whi'n'zh:during .the slowly varying jfor- "ward portions of vsaid sawtooth .;oscillat ions.;.the 'oi-sai'd amplifier. is reduced-whilst duringthe 1 rapid return portions of said sawtooth oscilla- "-tions 'the gain 'ofvsaid amplifier is. increased so that 'th'e rapidity of the :return .zp'ortions ,i increased compared with .what iitzwould :be;if:.the "gain of said amplifieriwere not :increased. According toanotherlfeature or; the invention th'ere' is provided a circuit arrangement :for :gen- "erating clectrical sawtooth .vosc'illations which have slowly -varying forward-portions. and rapid "returnmportions comprising aniamplifierx arranged -to amplifiy the slowly varying portions of .;said oscillations and means ior rendering said .amplifie'r 'u'nstable at predetermined periods use: that the return portions of the sawtooth: oscillations aregenerated by virtueof anatural ioscillationof said amplifier. I

Accordingto-another feature of: the invention "there is provided a circuit-arrangement for generating electrical sawtooth oscillations which have flslowly varying forward portions and rapid return portions comprising -an-'ampl-ifier,-a nega- "tiv'e feedback path between an output circuit of said amplifier and an input circuit thereof-which is-operative "during the slowly varying portions of said'sawtooth' oscillations-and means for rendering' said negative feedback path-substantially ine'ffective during therapid return portions of said sawtooth oscillations. r V

In order that the invention may-be more clearlyunderstood and readily carried into effect, it will now be described with reference to the accompanyingi'drawing which illustrates one embodiment of a circuit according to the invention. Referring to the drawingjjwhi'ch shows'a circuit arrangement for feeding "the magnetic defiection coils of a cathode-ray tube with sawtooth .ccurrent variations,- a condenser I is connected through a charging resistor 2 to -,a;'s0urce .ofiinegative charging potential. -so that a negative charge builds. up, on. the condenser and generates 4a.: substantially linear. forward; portion of :a saw- *1 tooth=oscillation .The condenser I is "discharged :periodical1y..by.aLdiode. 3 v,jwhich. is rendered perisa series resistorw23 across which 15. .develqpfid a .odically ,conduc'tinglby loontrollinjg f assume-i4 .so that sawtooth 'oscillationsj'of poten- ..tiai. are set up atthe, junction; between condenser set .u

e mm l and resistoriZ. .c g V Thesaiwtooth oscillations areg appliecl toth e control electrode of an amplifier valve'ithe am- .plifie'd output from which, set-11p-across'the load resistor 5,.is' applied ftothe control electrode 'of a'iurthe'r amplifier valve "Ii through all C. coupling network 8. The control electrode oi valve 1 is biased via resistor. 9 and a cathode resistor l0 :is',p1:ovided 'for lineariz ingathe characteristic of said valve. The amplified iioutputf jrom 1valve f! p, across itsi'l'o'a'd. resistor?! l is applied to the control ,lect'r'oide oian amplifier valv 71 2 via coupling resistor Ii'3. "The controlel'ectrode of valve l2'is lbiasedthrough' resistorflj ljarid a cathode resistor "I5 is I provided for 'linearizing the characteristic 'oisaidivalve. This amplifier valve "I 2 feeds deflecting 50011816 through a transformer having a primarvwindin'g H and a sec'ondary winding l9 and the control applied tolsaidcontrol electrode of valve '12 :is'in 'such sense that said electrode is loweredfjin' potential during; the

forward portions or the sawtooth oscillations. In series with the primary Winding" H1 is asm'all resistor l8 j'from which negative Qcurrentieedback. may be j derived andjappliedtou the control electrode .of.valve"l'. A diojde 201' is connected'beitween [the I anode and control electrode of {'the valve [2 in the manner jshown so that 1 it "becomes conducting whenjthe control. electrode of valve l2 fallsin potential. The anode of "the diode 201s connectedtolltheqanodejofgthe valve 1 2 viada condenser}! a leak resistor-121 also being provided lasIshown. lThus, during thejforward portions of the sawtooth-oscillations,"the amplifier valve 1 2. has a. large, portion, of its outvput applied to its input insa, degenerative sense so that its. gain is. small. .Anode current oijthe .valve l2, flowing, in: theprim'ary winding "ll of saidtransformer,v induces .anzelectromotive force in the: secondary winding. I 9 .whichiin turn QauSls a sawtooth current tojfiow. in coils; l6. ",Inclufded in the path of .the current. throughlthe .coilsjjl 6 voltage proportional :to the output currennand this voltage. is .appliedin aldegenerative sense to the charging condenser I. in. orderto. make. more .nearly linear. the forwardiportion of the sawtooth .impulseat thaanodeof dischargedio'defi thepotential oithe controlelectrode oflamplifiervalve l;2 is raised thus causing the diodeviflwto become non-conducting. Consequently. substantially lino degenerative circuit exists directly between, the

.input and output electrodes of :the valve ligand,

3, .V the gain of'said valve rises accordingly. Owing consequently to the high amplification of the circuit comprising amplifier valves 5, 1 and I2 and to the presence of the feedback path through the condenser l, the circuit becomes unstable and the rapid return portions of the sawtooth voltage;

are thus set up as regenerativ half-cycles of oscillation at the natural frequency of the circuit. At the end of a half-cycle of natural oscillation the diode becomes conducting and renders the circuit stable and so prevents the persistence of the regenerative oscillations. The circuit accordingly then commences to generate the forward stroke of another sawtooth oscillation.

I claim:

1. A circuit arrangement for generating elecit'ricalsawtooth oscillations, comprising a variable .gainamplifier, means for controlling said amplifier' t'o'amplify the slowly varying forward portions of said sawtooth oscillations, a unidirectionally conducting device connected to said amplifier, and .meansforlvarying the conductivity of said device for increasing the gain of said amplifier during" the rapid return portions of said sawtooth oscillations to increase return portions.

2. A circuit arrangement for generating electrical sawtooth oscillations, comprising an amplifierhaving a stable and anunstable condition, means for controlling said amplifier to'amplify -the slow1y varying forward portions of said sawtooth oscillations whilst said amplifier is in a stablecondition, and means for rendering said amplifier unstable at predetermined periods to produce natural oscillations and consequent generation of the return portions of the sawtooth oscillations.

' A circuit arrangement for generating electrical sawtooth oscillations, comprising an amplifier, a negative feedback path between an output circuit of said amplifier and an input circuit thereof, means for controlling said amplifier to amplify the slowly varying forward portions. of said sawtooth oscillations whilst said negative feedback path is operative, and means the rapidity of the 4 ally conducting deviceficofinected' to; and amplifier for controlling said stable and-unstable conditions of said amplifier, and means for controlling said unidirectionally conducting device to change the condition of said amplifier from the stable to the unstable condition at predetermined periods to cause said amplifier to produce natural oscillations and consequent generation of the return portions of the sawtooth oscillations.

6. A circuit arrangement for generating electrical sawtooth oscillations, comprising an amplifier, 'a negative feedback path between an output circuit of said amplifier and an input circuit thereof, a unidirectionally conducting device connected to said amplifier for switching said negative feedback path in to and out of operation, means for controlling said amplifier to amplify the slowly-varying forward portions of said sawtooth oscillations whilst said unidirectionally conducting device'is ina condition to make said negative feedback path operative, and means for switching said unidirectionally conducting device to cause said negative feedback path to be renderedinoperative to increase the gain of said amplifier during the rapid return portions of said sawtooth oscillations.

7. A circuit arrangement for generating elec- "tricalsawtooth oscillations, comprising an am? forrendering said negative feedback path substantially ineffective to increase the gain of said f amplifier during the rapid return portions of 'I said sawtooth oscillations.

' 4. A circuit arrangement for generating electrical sawtooth oscillations, comprising a variable ,gain amplifier, a storage device, means for charging said storage device to generate the .slowly varying portions of said sawtooth oscillations, means for periodically discharging said storage device, means for feeding the output of said storage. device to said amplifier to cause said amplifierto amplify the slowly varying forward portions of said sawtooth oscillations, a unidirectional1y conducting device connected to said amplifienmeans for maintaining said unidirectionally conducting device in a condition to maintain the gain of said amplifier low during said slowly varying portions, and means for changing the condition'of said unidirectionally conducting device when said storage device is I discharged to increase the gain of said amplifier during the rapid return portions of said sawtooth oscillations.

5. Acircuit arrangement for generating electrical sawtooth oscillations, comprising an amplifier havinga stable and an unstable condition,

means for feeding to said amplifier slowly varying forward portions of said oscillations whilst said amplifier is in a stable condition, a unidirectionplifier having. a stable and an unstable condition, a storage device, means for charging said storage device to generate the slowly varying portions of said sawtooth oscillations, means for discharging said storage device at predetermined periods, a unidirectionally: conducting device connected to said amplifier for controlling said stable and unstable conditions, means for feeding the output of said storage device to said amplifier to amplify the slowly varying forward portions of said oscillations whilst said amplifier is in a stable condition, and means for con- .trolling' said unidirectionally conduotingdevice to change said amplifier from the stable to the unstable condition when said storage device is discharged to'produce natural oscillations and consequent generation of the return portions of I the sawtooth oscillations.

8. A circuit arrangement according to claim 7,

, including a negative feedback path between an EDWARD ARTHUR v REFERENCES CITED Y The following'r'eferenc'es are of record in the H file of this patent:

UNITED STATES PATENTS Date Number Name 2,241,762 Blumlein May 13, 1941 2,251,851 Moore Aug. 5, 1941 2,265,290 Knick i. Dec. 9,1941 2,284,378 Dome May.'26,"1942 2,296,727 Moore J Sept. .22, .1942 2,309,672 Schade Feb. 2.19 43 

